Hydrogen-Mediated Thin Pt Layer Formation on NiN Nanoparticles for the Oxygen Reduction Reaction.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (NiN) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the NiN core, hydrogen molecules (H) were used as a mild reducing agent. As H oxidation is catalyzed by the surface of NiN, the redox reaction between H and Pt(IV) in solution was facilitated on the NiN surface, which resulted in the selective deposition of Pt on NiN. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the NiN core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on NiN nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.